318 POULTRY BREEDING AND MANAGEMENT 



air is given off, and in passing out of the shell these im- 

 purities aid in its decomposition; they dissolve certain food 

 in the shell, mineral nutrients, that the chick uses in the 

 growth of its body, and without which it would not come 

 to life. The impurities or poisons are contained in the car- 

 bonic acid gas given off by the chick, or exhaled by the 

 lungs. This thing that poisons the body is used by the 

 chick to dissolve the mineral elements of the shell needed 

 in the growth of its body. The shell is honeycombed, so 

 to speak, by this gas that has been cast off by the chick, 

 and the dissolved elements pass into its'body. Without the 

 lime extracted from the shell the chick would not have the 

 strength to break through the shell, or breaking through 

 would not have vitality to live. 



More than that, the chick utilizes materials in the shell 

 itself for arming itself with a weapon concealed on the 

 point of its beak to puncture a hole in its prison wall and 

 escape. 



Carbonic acid gas has an important function to perform 

 in the development of the embryonic life of the chick. A 

 healthy, strong-growing embryo is giving off considerable 

 quantities of this gas, and this gas in passing through the 

 pores of the shell dissolves the necessary minerals for the 

 nutrition of the chick. As the chick grows there is an in- 

 crease in the amount of carbon dioxide thrown off. Analysis 

 showed more carbon dioxide in the incubator in the later 

 stages of incubation than in the first. Analysis further 

 showed more carbon dioxide under the sitting hen than in 

 the incubator. There was a large amount found under the 

 hen when sitting on glass or china eggs, which led to the 

 discovery that carbon dioxide was being diffused through 

 the skin of the hen's body. 



It has not yet been determined whether the same quantity 

 of carbon dioxide must be present in the incubator as under 



